The invention relates to an antenna transponder configuration for angle measurement, torque measurement, data transmission for angle position determination, signal preprocessing and angle measurement using a rotating encoder for such a configuration.
In order to measure the angle and position of a rotating shaft, Published, European Patent Application EP 0 611 952 A1 discloses an apparatus in which a sequence of different permanent magnets is provided on a ring which surrounds a rotating shaft. The sequence is coded, so that the position of the shaft can be deduced from the sequence of magnetic polarities. A stationary angle sensor is provided in order to detect the shaft position and, by interaction with the permanent magnets, produces a signal sequence from which the shaft position can be deduced. The apparatus has the disadvantage that permanent magnets must be provided on a shaft, and their polarity can be changed by strong external magnetic fields. Furthermore, the ring requires a certain physical extent in order to provide the various individual magnets. Furthermore, it is impossible to transmit power from the angle sensor to the shaft in order to supply further measurement sensors, for example for torque measurement, there.
International Patent Disclosure WO 95/31696, corresponding to U.S. Pat. No. 5,815,091, describes a linear position identification system, which has a stationary antenna device with a pair of spiral coils and an excitation coil. In this case, the mean flux from the two spiral coils cancels itself out. Currents are induced in the spiral coils by use of a tuned circuit having a resonant response, and the amplitude of these currents represents a measure of the position of the tuned circuit.
In addition, antenna transponder configurations are known in which power is transmitted from a stationary antenna to a rotating transponder, and the position of the transponder can be measured as a result of at least one coil element of the stationary antenna having a meandering form. Such configurations provide a meandering antenna for detecting the angle position. The electromagnetic coupling to the environment is very high due to the large area enclosed by the stationary coil. Therefore, a large amount of power is required to produce a desired magnetic field intensity. In addition, the interference emission to the environment is high and, finally, the sensitivity to radiated interference in the primary circuit is high.
It is accordingly an object of the invention to provide an antenna transponder configuration for power transmission and angle measurement that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which it is possible to determine the position of a rotating transponder relative to a stationary antenna device as accurately as possible and with as little sensitivity to interference as possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, an antenna transponder for angle measurement and data transmission. The antenna transponder is formed of a stationary antenna device having at least two concentric coils with different mean radii and each of the two concentric coils have an interior. At least one of the two concentric coils is a meandering coil and mean flux in the interior of the two concentric coils approximately cancels itself out. A rotatable part is disposed opposite the stationary antenna device. A transponder is disposed on the rotatable part, and the stationary antenna device and the transponder define an air gap there-between.
At least two coils are used in the stator (stationary antenna device) and lead to alternating magnetic fluxes along a predetermined radius, which is also the rotation radius of the rotor (with the transponder). In this case, the coils of the stationary antenna device are configured and are provided with current of the known polarity such that the resultant field in the innermost area, which is common to all the coils, largely cancels itself out. The configuration can be configured such that one coil is in the form of a meandering coil and the other is smooth, such that two coils are smooth and one is meandering, or such that there are two meandering coils. This results in a reduction in the inductance, the susceptibility to radiated interference, and the radiated emissions of the configuration. If we regard the antenna coils as the primary of a transformer with a large air gap, and the coils of the rotor as the secondary of a transformer, then, to a first approximation, the amount of coupling is proportional to the superimposed areas. A coupling level of 1 would be desirable, but this can never be achieved. Reducing the magnetically active area of the primary coil configuration considerably increases the amount of coupling for a given, constant secondary coil area.
A further problem with such configurations is the major reduction in the amount of coupling as the air gap becomes larger, with the voltage induced in the secondary likewise then decreasing to a major extent. This is a poor precondition for accurate position determination. In order to improve this phenomenon, the position measurement is based on a ratio measurement. This is done by comparing the voltage U1, which represents the position, with the comparison voltage U2, with both voltages being equally proportional to the air gap.
In accordance with an added feature of the invention, a shaft is provided on which the rotatable part is connected. A torque sensor is further provided. The transponder detects measured torque data from the torque sensor, a torque being transmitted on the shaft and the shaft is mounted such that it can rotate. The transponder transmits the measured torque data to the stationary antenna device.
In accordance with an additional feature of the invention, an evaluation circuit is electrically conductively connected to the transponder and evaluates the measured torque data from the torque sensor. The transponder has a coil for supplying power to the evaluation circuit, a voltage induced by the coil is rectified and passed to the evaluation circuit.
In accordance with another feature of the invention, the transponder transmits a first measured variable being a resistive part, and a second measured variable being a capacitive part, to the stationary antenna device.
With the foregoing and other objects in view there is provided, in accordance with the invention, a combination of a manufactured device with an antenna transponder for measuring an angular position of the manufactured device. The antenna transponder contains a stationary antenna device having at least two concentric coils with different mean radii and each of the two concentric coils have an interior. At least one of the two concentric coils is a meandering coil and a mean flux in the interior of the two concentric coils approximately cancels itself out. A rotatable is part disposed on the manufactured device. A transponder is disposed on the rotatable part, and the stationary antenna device and the transponder defining an air gap there-between. A first operating state which exists once the manufactured device is started up and represents a learning state of the manufactured device, and a second operating state corresponding to a normal operation of the manufactured device are derived, the first operating state and the second operating state are taken into account by comparing them for adapting a measured angle position signal to possible manufacturing inaccuracies of the manufactured device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an antenna transponder configuration for power transmission and angle measurement, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.